GRADE STRUCTURE. Chemical pulps (sulfate, sulfite, soda, cotton linters, or vegetable fiber) are used to make uncoated free-sheet papers, with occasional additions of up to 10% mechanical fiber or bleached chemithermomechanical (BCTMP) pulps and recycled fibers. BCTMP purnishes lower the cost of manufacture while providing a better grade of paper than stone groundwood or other mechanical pulps. Many major producers have converted some or all machines to alkaline-based paper, and most new installations are alkaline.
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